Methods of scale inhibition using substoichiometric amounts of amino alcohol and phosphonic acids

ABSTRACT

The precipitation of scale-forming materials in an aqueous system is inhibited by adding substoichiometric amounts of a precipitation inhibitor which consists of a mixture of an amino alcohol such as triethanolamine and certain phosphonic acids, such as amino tri(methylene phosphonic acid), to said system.

United States Patent Kowalski [4 1 June 20, 1972 METHODS OF SCALE INHIBITION USING SUBSTOICHIOMETRIC AMOUNTS OF AMINO ALCOHOL AND PHOSPHONIC ACIDS Xavier Kowalski, Creve Coeur, Mo.

Assignee: Monsanto Company, St. Louis, Mo.

Filed: Sept. 10, 1970 Appl. No.: 71,245

Inventor:

U.S. Cl. ..252/18 D, 2 H27, 134/2, 210/58, 252/80, 252/86, 252/175, 252/181 Int. Cl. ..C02b 5/06 Field ofSearch ..252/181, 80, 82, 86, 117, 152, 252/156, 175, 180; 210/58, 59; 21/2.7; 134/2 References Cited UNlTED STATES PATENTS 8/1967 Ralston ..252/180 X Primary Examiner-John T. Goolkasian Assistant Examiner-M. E. McCamish Attorney-Herbert B. Roberts, James J, Mullen and Neal E. Willis [57] ABSTRACT The precipitation of scale-forming materials in an aqueous system is inhibited by adding substoichiometric amounts of a precipitation inhibitor which consists of a mixture of an amino alcohol such as triethanolamine and certain phosphonic acids, such as amino tri( methylene phosphonic acid), to said system.

10 Claims, No Drawings METHODS OF SCALE INHIBITION USING SUBSTOICHIOMETRIC AMOUNTS OF AMINO ALCOHOL AND PHOSPHONIC ACIDS METHODS OF SCALE INHIBITION This invention relates to methods for inhibiting the precipitation of metal ions from aqueous solutions, and more particularly, to the use of a mixture of certain amino alcohols and phosphonic acids to accomplish this purpose.

Most commercial water contains alkaline earth metal cations, such as calcium, barium, magnesium, and transition metals such as iron or copper, etc., and several anions such as bicarbonate, carbonate, sulfate, oxalate, phosphate, silicate, fluoride, hydroxides, etc. When combinations of these anions and cations are present in concentrations which exceed the solubility of their reaction products, precipitates form until their reaction solubility product concentrations are no longer exceeded. For example, when the concentrations of calcium ion and sulfate ion exceed the solubility of the calcium sulfate, a solid phase of calcium sulfate will form. Similarly an iron hydroxy material will form and precipitate.

Solubility product concentrations are exceeded for various reasons, such as evaporation of the water phase, change in pH, pressure or temperature, and the introduction of additional ions which form insoluble compounds with the ions already present in the solution.

As these reaction products precipitate on the surfaces of the water carrying system, they form scale. The scale prevents effective heat transfer, interferes with fluid flow, facilitates corrosive processes, and harbors bacteria. The presence of this scale is an expensive problem in many industrial water systems, oilwells, and the like, causing delay and shutdowns for cleaning and removal. Scale-forming compounds or materials can be prevented from precipitating by inactivating their cations with chelating or sequestering agents, so that the solubility of their reaction products is not exceeded. Generally, this requires many times as much chelating or sequestering agent as cation, and these amounts are not always desirable or economical.

More than twenty-five years ago it was discovered that certain inorganic polyphosphates would prevent such precipitation when added in amounts less than the concentrations needed for sequestering or chelating. See, for example, Hatch and Rice, Industrial Engineering Clzemislry, vol. 31, pages l and 53; Reitemeir and Buehrer, Journal of Physical Chemistry, vol. 44, No. 5, pages 535 and 536 (May 1940); Fink and Richardson U.S. Pat. No. 2,358,222; and Hatch U.S. Pat. No. 2,539,305, all of which are incorporated herein by reference. For sequestration, the mole ratio of precipitation inhibitor equivalents to scale forming cation is usually 0.5:1 to 1:1 or greater (2:1, 3:1, etc.). These ratios are referred to as stoichiometric. The present invention is concerned with substoichiometric amounts of a precipitation inhibitor. Substoichiometric amounts would include all mole ratios of precipitation inhibitor equivalent to scale forming cation that are less than the level required for sequestration. The use of substoichiometric amounts in the water treating art is generally referred to as the threshold" treatment of water; note U.S. Pat. No. 3,336,221 which is incorporated herein by reference.

The substoichiometric concentration range can be demonstrated in the following manner. When a typical scale-forming solution containing the cation of a relatively insoluble com pound is added to a solution containing the anion of the relatively insoluble compound and a very small amount of a substoichiometric active inhibitor, the relatively insoluble compound will not precipitate even when its normal equilibrium concentration has been exceeded.

The polyphosphates are generally efiective substoichiometric precipitation inhibitors for many scale-forming compounds. After prolonged periods at higher temperatures, however. they lose their effectiveness. ln an acid solution, they revert to ineffective or less effective compounds.

Accordingly, an object of this invention is to provide a method for inhibiting the precipitation of metal ions from aqueous solutions.

Another object of this invention is to provide a precipitation inhibitor which is effective in inhibiting the precipitation of heavy metal ions in alkaline aqueous solutions.

A still further object of this invention is to provide a precipitation inhibitor which is effective, when used in threshold amounts, in inhibiting the precipitation of iron ions in alkaline solutions.

Other objects will become-apparent from a reading of the following detailed description and appended claims.

1t has been found that mixtures of certain amino alcohols and certain phosphonic acids unexpectedly function as superior precipitation inhibitors when used in substoichiometric concentrations, i.e., in threshold amounts, in aqueous systems.

lt is to be understood that the term precipitation inhibitor" as used herein means a mixture of the amino alcohols and phosphonic acids.

The amino alcohols which are found effective with said phosphonic acids are mono-, diand triethanolamine; mono-, diand tris-isopropylamine; monoand di-isobutanolamine; butanolamine; dibutyl amino ethyl alcohol; dibutyl amino propyl alcohol; dibutyl amino isopropyl alcohol; bis( 2-hydroxyethyl) butyl amine; butyl ethyl 2,2 dihydroxy amine; dibutyl ethyl 2,2',2" trihydroxy amine; bis(2-hydroxyethyl) methyl amine and dipropyl ethyl 2,2,2 trihydroxy amine. The preferred amino alcohol for use in this invention is triethanolamine.

The phosphonic acids which are found effective with the amino alcohols are I l. l-hydroxy ethylidene-l,1 diphosphonic acid (referred to herein as HEDP) 2. amino tri(methylene phosphonic acid) (referred to herein as ATMP) 3. ethylene diamine tetra( methylene phosphonic acid) (referred to herein as EDTMP) 4. hexamethylene diamine tetra( methylene phosphonic acid) (referred to herein as HDTMP) The phosphonic acids set forth above can be prepared according to the processes described and claimed in US. Pat. No. 2,599,807, U.S. Pat. No. 3,288,846, and U.S. Pat. No. 3,504,018, all of which are incorporated herein by reference.

lt is to be understood that the term phosphonic acids as used herein means those acids set forth above and the salts thereof, particularly the water-soluble salts. Typical salts of these phosphonic acids include, without limitation, the alkali metal (such as sodium, lithium and potassium); alkaline earth metal (such as calcium and magnesium); zinc, ammonia and alkyl ammonia salts.

The weight ratio of phosphonic acid to amino alcohol in the carried out. Measured volumes of concentrated NaCO and Na SO are individually and separately added to solutions containing calcium chloride and the desired precipitation inhibitor, which is indicated by the reference number 2, 4, 6, 8 and precipitation inhibitor is less than :1, preferably less than 3:1 5 in the first column of Table l. The temperature of the and more preferably less than 1:1. The preferred ratio is from resul ant solutions and the pH are also shown in Table I. The 0-2511 about 311. time necessary for visual observation of significant amounts of It has also been found that the mixtures of phosphonic acids precipitate is called the "Time to Failure." in conjunction and amino alcohols are quite effective precipitation inhibitors with the calcium sulfate studies, the CaC1.,NaCl-precipitawhen used in threshold amounts in aqueous solutions con- 10 tion inhibitor solutions are heated to 95 C. in reflux before taining iron ions and calcium and magnesium ions. In the the sodium sulfate is added. The results of these tests are set aqueous alkaline solutions, the pH is usually above 6.0, forth in Table I. generally in the range of6.5 to 12. In conjunction with the results set forth in Table l, the The precipitation inhibitors of the instant invention exhibit, blank additive did not contain any precipitation inhibitor and in addition to their scale preventing ability, the highly beneficonsequently is utilized as a control. The amino alcohol and cial properties of being highly water soluble and hydrolytically phosphonic acid (used individually) additives are indicated by stable, that is, having a substantial resistance to hydrolysis or the reference numbers 1, 3, 5, 7, 9, l l and 12. The utilization degradation under various pH and temperature conditions. of the particular present invention precipitation inhibitors is Although the precipitation inhibitors of the present inven- 2O vividly demonstrated in that the use of these precipitation intion are of general utility whenever it is desired to inhibit the hibitor a hown results in an unexpected effectiveness as a precipitation of metal ions from aqueous solutions, they are precipitation inhibitor as compared to the use of either the especially effective in such applications as liquid soaps and amino alcohols or phosphonic acids individually. The utility of shampoos, bar soaps, scouring wool cloth, cotton scouring,, these precipitation inhibitors thus is uniquely demonstrated.

TABLE I [Amino alcohols plus phosphonic acids as precipitation inhibitors] Time to failure Gil-C03 CHCO; CtlSOi C3804 (6,500 ppm.) (400 ppm.) (6,500 ppm.) (8,500 p.p.m.) 0., pII:7, 25 0., pl1=10, 25 (3., pH: 05 0., pl[::7.5. Additive Weight 2 ppm. 2 p.p.m. 2 ppm. 2.7 ppm. (rel. No.) Additive ratio 1 additive additive additive additive Blank 4 min 6 min 1 hr 5n1iu. Ti'it'thanolaniiuu 3 days 2 days 14 days 60 min. Triethanolamine plus lIEDI 1:1 21 days 16 days 28 days. 2 days. 11'isisop10py1an1iue 3 days. 3 days 8 days... 00min. Tris-isopropylamine plus ATM 1:1 18 days. 17 days. 24 days. 3 days. Butanolamine. 4days 2dii s 5 (lays 60 min. 6 Butauolamine plus EDTMP 1:1 26 days 15 days 7 Dibutyl amino propyl alcohol". 1 3 days 2 days 8 Dibutyl amino propyl alcohol plus HDIMP. 1:1 1 U Bis(2-hydroxyethyl) methylamine 1 A 3 days. 0 Bis(2-l'iydroxyethyl) methylamine plus IlElJP 1:1 1 11 HEMP tidays 4days 12 H ATMP 7 1 Weight ratio of phosphonic acid (100% active basis) to amino alcohol.

cotton dyeing, cotton bleaching, metal cleaning compounds, rubber and plastics trace metal contamination (compounding and polymerization), pulp and paper trace metal contamination, toilet bowl cleaners, disinfectants, and dispersants.

The amount of the precipitation inhibitor necessary to be effective varies with, inter alia, the type and amount of problem metal ions, pH conditions, temperature and the like, but in all cases, substoichiometric (threshold) amounts are used. The mole ratio of the precipitation inhibitor to the scale forming cation material is generally greater than about 1:2 and preferably from about 1:25 to about 1: 10,000.

The precipitation inhibitors work quite effectively in the range of 0. 1 to 500 parts per million parts of total solution.

it is of interest to note that a large percentage of sequestering agents (stoichiometrically used in application) do not work effectively when used in substoichiometric amounts. Examples of the latter class are ethylene diamine tetramine, nitrilotriacetic acid and salts, and gluconic acid. Also, there are many alcohols and diols which do not work at all, e.g., phosphorylated ethane diol, phosphorylated 1,4-n-butane diol, and H,O;,PO(CH,) OPO H The following examples are included to illustrate the practice of the invention and the advantages provided thereby but are not to be considered limiting. Unless otherwise specified, all parts are parts by weight and all temperatures are in degrees Centigrade.

EXAMPLEI In order to demonstrate the unique properties of the present invention precipitation inhibitors, the following procedure is EXAMPLE 11 The above Example 1 is repeated several times with the concentration of the specific precipitation inhibitor (additive) being respectively 25 ppm, ppm, 200 ppm and 500 ppm and the weight ratios (phosphonic acid to amino alcohol), at each ppm level, being 1:1 and 0.5:1. The results utilizing these ppm concentrations and weight ratios are similar to the results obtained in Example 1.

EXAMPLE 111 in order to demonstrate the effectiveness of triethanolamine and ATM? or HEDP as a threshold agent (precipitation inhibitor) in treating iron ion-containing water (which also contains calcium and magnesium ions), the following procedure is carried out.

Measured amounts of the precipitation inhibitor as indicated in Table II are added to a 500 milliliter beaker containing 300 milliliters of water at 25 C. in order to prepare the, indicated concentrations. The pH of each solution is adjusted to pH 10 by adding sodium hydroxide. in sequential order, measured amounts of calcium chloride, magnesium chloride and ferric chloride are added with stirring to each alkaline solution in order to provide a resultant solution with the indicated molar ratios. The time necessary for visual observation of significant amounts of precipitate is called the Time to Failure." These times are recorded and shown in Table II.

In conjunction with the results set forth in Table 11, the blank" solution did not contain any precipitation inhibitor and consequently is used as a control. The first three solutions,

after the blank, contained only triethanolamine, but in different concentrations. The next three solutions contained individually the well known threshold agents l hydroxy ethylidene-l,l-diphosphonic acid (HEDP) (2 and 4 ppm respectively) and amino tri(methylene phosphonic acid) (ATMP); note US. Pat. No. 3,214,454 and U.S. Pat. No. 3,336,22l, respectively (both of these patents are incorporated herein by reference).

The remaining two solutions contained the present invention precipitation inhibitors, e.g., TEA HEDP and TEA ATMP.

The results of this Example iii are readily seen. The triethanolamine (TEA) per se exhibited a substantial effectiveness as a threshold agent for inhibiting the precipitation of iron as compared to the blank or control." Furthermore, this amino alcohol (TEA) demonstrated that it is as effective (on a comparative basis) as the well known threshold agents HEDP AND ATMP in conjunction with the prevention of the precipitation of iron from aqueous alkaline solutions containing calcium and magnesium ions. However, the combination of the amino alcohol and phosphonic acids (ATMP or HEDP) yield results which were quite unexpected. Furthermore, one having skill in the water treating art would not anticipate that such unique results would naturally flow from a mere combination of the amino alcohol and phosphonic acid when such a phosphonic acid as ATMP is somewhat ineffective in preventing the precipitation of iron salts.

stoichiometric amounts of a mixtu and (2) a phosphonic acid selecteJfrSfiftbbfi'StifiZZrfiiiZ? of (a) amino tri(methylene phosphonic acid), (b) l-hydroxy ethylidene-l diphosphonic acid, (c) ethylene diamine tetra- (methylene phosphonic acid, (d) hexamethylene diamine tetra-(methylene phosphonic acid) and (e) salts of said acids to said system.

2. The method of claim 1 wherein the scale-forming material is selected from the group consisting of alkaline earth metal carbonates, sulfates, oxalates, phosphates, fluorides, silicates, transition metal hydroxides, or mixtures thereof.

3. The method of claim 1 wherein the mole ratio of precipitation inhibitor to scale-forming cation material is from about 1:2.5 to about 1210,000.

4. The method of claim 1 wherein the amino alcohol is triethanolamine and the weight ratio of phosphonic acid to amino alcohol is from about 0.25:1 to about 1:1.

5. The method of claim 4 wherein the scale-forming materi al is an iron hydroxy compound.

6. The method of claim 4 wherein the precipitation inhibitor is present in the system at concentrations from about 0.l part per million to about 500 parts per million.

7. A method of inhibiting the precipitation of iron hydroxy compounds in an alkaline aqueous system containing calcium and magnesium ions, comprising adding threshold amounts of a mixture of triethanolamine and amino tri(methylene phosphonic acid) to said system.

TABLE II [Triethanolamine plus HEDP or ATMP as threshold agents] P M 1 RMglar C .p.m. in 0 es in a ios Fe 1 'Ii t Precipitation inhibitor (PI) solution 1 solution 2 CaClgzPI MgClzzPl 3 failt fi 0 Blank 0 Triothanolamine (TEA) 1 min Do 2 2 70 min 4 75 min 2 min 3 min TEA plusIIEDP 2 I 3 Z .5 .1 5 h TEA plus AIMP 2 6- 7X10 45. 5511 2). 29:1 26. 29:1 3% i'1 b grs 1 Parts of precipitation inhibitor on a 100% 2 Moles of precipitation inhibitor in solution.

3 l-liydroxy ethylidene-l,l-dipllosphonic acid.

4 Amino tri(methylene phosphonic acid).

5 Weight ratio HEDP:TEA is 1:1; HEDP, 100% active basis.

0 Weight ratio ATMP:TE A is 1:1; 1 00% act ive basis.

The foregoing examples have been described in the foregoing specification for the purpose of illustration and not limita-- tion. Many other modifications and ramifications will naturally suggest themselves to those skilled in the art based on this disclosure. These are intended to be comprehended as within the scope of this invention.

What is claimed is:

l. A method of inhibiting the precipitation of scale-forming materials in an aqueous system comprising adding subactive basis per one million parts of solution.

8. A method of claim 7 wherein the alkaline aqueous system has a pH of from about 6.5 to about 12.

9. The method of claim 8 wherein the mole ratio of said mixture to iron hydroxy compound is from about 1:25 to about l:l0,000.

10. The method of claim 8 wherein the mixture is present in the system at concentrations from about 0.1 part per million to about 500 parts per million. 

2. The method of claim 1 wherein the scale-forming material is selected from the group consisting of alkaline earth metal carbonates, sulfates, oxalates, phosphates, fluorides, silicates, transition metal hydroxides, or mixtures thereof.
 3. The method of claim 1 wherein the mole ratio of precipitation inhibitor to scale-forming cation material is from about 1:2.5 to about 1:10,000.
 4. The method of claim 1 wherein the amino alcohol is triethanolamine and the weight ratio of phosphonic acid to amino alcohol is from about 0.25:1 to about 1:1.
 5. The method of claim 4 wherein the scale-forming material is an iron hydroxy compound.
 6. The method of claim 4 wherein the precipitation inhibitor is present in the system at concentrations from about 0.1 part per million to about 500 parts per million.
 7. A method of inhibiting the precipitation of iron hydroxy compounds in an alkaline aqueous system containing calcium and magnesium ions, comprising adding threshold amounts of a mixture of triethanolamine and amino tri(methylene phosphonic acid) to said system.
 8. A method of claim 7 wherein the alkaline aqueous system has a pH of from about 6.5 to about
 12. 9. The method of claim 8 wherein the mole ratio of said mixture to iron hydroxy compound is from about 1:2.5 to about 1:10,000.
 10. The method of claim 8 wherein the mixture is present in the system at concentrations from about 0.1 part per million to about 500 parts per million. 